Diabetic nephropathy (DN) is one of the major complications of diabetes that can lead to end stage renal disease. The rates of DN are escalating and new strategies are needed to combat this debilitating condition. Key features of DN include increased glomerulosclerosis and mesangial cell expansion due to the accumulation of extracellular matrix (ECM) proteins. Although several biochemical pathways and key profibrotic factors, such as transforming growth factor-b1 (TGFb1) and the ECM protein collagen, have been implicated in the pathogenesis of DN, the subtle molecular mechanisms regulating them are unclear. In the previous funding period we identified new roles for renal microRNAs (miRNAs) in the pathogenesis of DN. We demonstrated that miR-192 can mediate TGF b1 induced collagen expression in mesangial cells (MCs), and that miR-192 deficiency can protect against key features of DN in mouse models. Since then, renal miRNAs have gained increased attention in various renal diseases, and are also being recognized as promising clinical biomarkers for DN. However, we still have only limited knowledge about the spectrum of miRNAs that modify DN progression and their therapeutic potential. Our objective is to address this gap in knowledge by identifying the roles of newly identified miRNAs and their host genes in the pathogenesis of DN, and translational approaches to harness their potential to meet the critical need for better therapies for DN. We will follow up on extensive new preliminary data showing that a novel Mega Cluster of miRNAs is collectively up-regulated by TGFb1 and high glucose in vitro in MCs, and in diabetic mice glomeruli in vivo. Furthermore, we find that this cluster is embedded within a long transcript and both are regulated by stress responsive transcription factors, whereas target genes of multiple component miRNAs regulate protein translation, hypertrophy and cellular stress. The central hypothesis is that up-regulation of the mega cluster of miRNAs diabetic conditions suppresses the expression of their key functional gene targets, inducing glomerular MC hypertrophy, protein synthesis and fibrosis, and thereby augmenting DN progression. This hypothesis will be tested via three Specific Aims which will: i) examine the molecular mechanisms of regulation of key miRNAs within the mega cluster; ii) identify the functional roles of these miRNAs and key common target genes in MCs, and iii) finally evaluate novel gene targeting as well as translational approaches to down-regulate this miRNA cluster genomic region in mouse models of DN. The results of these conceptually innovative and clinically significant studies can define currently unknown regulatory factors in the diabetic kidney that could lead to the identification of critically needed new therapeutic targets for DN and thus have a positive impact to advance the field.